document workspace members
document workspace members

Summary:
This is a partial backport of [[https://github.com/bitcoin/bitcoin/pull/23381 | core#23381]]
https://github.com/bitcoin/bitcoin/pull/23381/commits/fd92b0c3986b9eb41ce28eb602f56d405bdd3cd7

Test Plan: read new  documentation

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D12352

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